A file server is a computer that provides file service relating to the organization of information on storage devices, such as disks. The file server or filer includes a storage operating system that implements a file system to logically organize the information as a hierarchical structure of directories and files on the disks. Each “on-disk” file may be implemented as a set of disk blocks configured to store information, such as text, whereas the directory may be implemented as a specially-formatted file in which information about other files and directories are stored. A filer may be configured to operate according to a client/server model of information delivery to thereby allow many clients to access files stored on a server, e.g., the filer. In this model, the client may comprise an application, such as a file system protocol, executing on a computer that “connects” to the filer over a computer network, such as a point-to-point link, shared local area network (LAN), wide area network (WAN), or virtual private network (VPN) implemented over a public network such as the Internet. Each client may request the services of the filer by issuing file system protocol messages (in the form of packets) to the filer over the network.
A common type of file system is a “write in-place” file system, an example of which is the conventional Berkeley fast file system. In a write in-place file system, the locations of the data structures, such as inodes and data blocks, on disk are typically fixed. An inode is a data structure used to store information, such as meta-data, about a file, whereas the data blocks are structures used to store the actual data for the file. The information contained in an inode may include, e.g., ownership of the file, access permission for the file, size of the file, file type and references to locations on disk of the data blocks for the file. The references to the locations of the file data are provided by pointers, which may further reference indirect blocks that, in turn, reference the data blocks, depending upon the quantity of data in the file. Changes to the inodes and data blocks are made “in-place” in accordance with the write in-place file system. If an update to a file extends the quantity of data for the file, an additional data block is allocated and the appropriate inode is updated to reference that data block.
Another type of file system is a write-anywhere file system that does not overwrite data on disks. If a data block on disk is retrieved (read) from disk into memory and “dirtied” with new data, the data block is stored (written) to a new location on disk to thereby optimize write performance. A write-anywhere file system may initially assume an optimal layout such that the data is substantially contiguously arranged on disks. The optimal disk layout results in efficient access operations, particularly for sequential read operations, directed to the disks. A particular example of a write-anywhere file system that is configured to operate on a filer is the Write Anywhere File Layout (WAFL™) file system available from Network Appliance, Inc. of Sunnyvale, Calif. The WAFL file system is implemented within a microkernel as part of the overall protocol stack of the filer and associated disk storage. This microkernel is supplied as part of Network Appliance's Data ONTAP™ storage operating system, residing on the filer, that processes file-service requests from network-attached clients.
As used herein, the term “storage operating system” generally refers to the computer-executable code operable on a storage system that implements file system semantics and manages data access. In this sense, Data ONTAP software is an example of such a storage operating system implemented as a microkernel. The storage operating system can also be implemented as an application program operating over a general-purpose operating system, such as UNIX® or Windows NT®, or as a general-purpose operating system with configurable functionality, which is configured for storage applications as described herein.
Disk storage is typically implemented as one or more storage “volumes” that comprise physical storage disks, defining an overall logical arrangement of storage space. Currently available filer implementations can serve a large number of discrete volumes (150 or more, for example). Each volume is associated with its own file system and, for purposes hereof, volume and file system shall generally be used synonymously. The disks within a volume are typically organized as one or more groups of Redundant Array of Independent (or Inexpensive) Disks (RAID). RAID implementations enhance the reliability/integrity of data storage through the redundant writing of data “stripes” across a given number of physical disks in the RAID group, and the appropriate caching of parity information with respect to the striped data. In the example of a WAFL file system, a RAID 4 implementation is advantageously employed. This implementation specifically entails the striping of data across a group of disks, and separate parity caching within a selected disk of the RAID group. As described herein, a volume typically comprises at least one data disk and one associated parity disk (or possibly data/parity) partitions in a single disk) arranged according to a RAID 4, or equivalent high-reliability, implementation.
Internally, the filer is a microprocessor-based computer in which one more microprocessors are interconnected by a system bus to various system components that may be physically located on a motherboard and which include a memory, having a buffer cache for storing data and commands, a network adapter for communicating over the LAN or another network, a firmware storage device such as an erasable programmable read only memory (EPROM—which may comprise a flash memory, that retains power during shutdown), that contains system firmware (including a boot mechanism), and various storage adapters for communicating with the storage volumes of the disk array attached to the filer.
New releases of the storage operating system may be issued for a variety of reasons, including, but not limited to correction of problems and addition of new features. In one known distribution method, the storage operating system is released on physical media, such as floppy disks. In another, the administrator may download the new version of the storage operating system from the producer's website over, for example, the well-known Internet. Each of these distribution methodologies has noted disadvantages. As the size of the storage operating system, or kernel, increases, the number of physical disks required to distribute the kernel also increases. Managing a set of, for example, ten floppy disks which contains the new version of the storage operating system can be cumbersome for system administrators.
A disadvantage shared by both the removable storage media and Internet-based distribution schemes is the possibility of corruption of the storage operating system during the installation process. For example, a power loss during the installation process could corrupt the storage operating system, thereby leaving the filer inoperative. In some implementations, the kernel or storage operating system may be contained on an EPROM or similar chip on the motherboard of the file server. However, these implementations have a noted disadvantage in that the storage capacity of these on-board chips is often too small to hold an entire copy of the storage operating system or kernel. Additionally, if an error or loss of power occurs during an upgrade process to an EPROM, the possibility of corruption of the kernel exists. Thus, it is desirable to quarantine the kernel or storage operating system during the upgrade process so that the kernel cannot be corrupted due to errors or power failures during the upgrade process.
Additionally, changes in the system configuration as a result of activating features to acquire additional functionality, such as enabling drivers or additional central processing units for multi-processing operation, can result in a non-operational system configuration. These non-operational system configurations can result from users adjusting or modifying a file server system configuration. Thus, it is desirable to quarantine a known configuration that is operational while the user or administrator modifies configuration variables.